The present invention relates generally to valves and to methods of producing puffs of gas and relates more particuarly to a valve which can both open and close very quickly and to a method of producing very well-defined puffs of gas.
In work in nuclear fusion, a great need has arisen for a fast-acting valve which can both open and close very quickly so as to produce a very sharply defined (i.e., short) puff of gas. Such a puff of gas is desirable for filling a theta pinch, wherein a controlled nuclear fusion reaction takes place, plasma in a long torus or skinny tube being confined by a magnetic field and shock-heated and compressed to produce the high temperatures at which fusion takes place. If a substantial tail is present on the gas puff used to fill a theta pinch, the plasma will cool and its lifetime will be limited. Therefore, a fast opening and fast closing valve is of great, if not critical, importance to a sustained, controlled fusion reaction.
A valve described as fast-opening was disclosed in the article by G. N. Aretov et al., "High-Speed Electrodynamic High-Pressure Gas Injector," Pribory i Tekhnika Eksperimenta, No. 3, pp. 219-222, May-June, 1972. However, upon close examination of that reference, it appears clear that the description in the reference does not lead one to the fast-opening and fast-closing valve of this invention which possesses two special features, both of which contribute to a fast closing. In fact, that article appears from the drawing even to teach away from at least one of these two features. Additionally, the valve in that article includes a spring; and the operation of that valve appears to be different from that of the present invention.
Valves which require springs to slow down and close the valves generally require frequent maintenance of the springs; and the valve housing must be quite large in order to house the spring when the valve is to move at very high speeds. For example, if a valve stem having a mass of 50 grams, a stem speed of 30 meters per second, and a maximum distance of stem travel of 4 millimeters must be stopped without damage to the valve solely by use of a spring, the spring would be required to have a spring constant of about 8 tons per inch. Considering that the coil springs of an automobile have spring constants of about one ton per inch, one can readily see that if a spring alone must stop the above-described valve stem, the spring would have to be very large and would require a very large housing in comparison with the size of the valve stem. Furthermore, when a spring is used in a valve to stop a valve stem, the valve stem is subject to bouncing; and this is highly undesirable when a well-defined puff of gas is sought. Furthermore, a linear spring would act to decrease the speed of the valve stem continuously as the spring is compressed, thus lengthening the opening time; and a short puff of gas could not be produced.